Hundreds of people come together at Place de la Bourse to mourn on Wednesday evening, March 23, 2016 (AP Photo/Martin Meissner)

People hold a banner showing the Brussels mascot defusing a bomb at Place de la Bourse on Wednesday evening, March 23, 2016. Bombs exploded yesterday at the Brussels airport and one of the city's metro stations, killing and wounding scores of people, as a European capital was again locked down amid heightened security threats. (AP Photo/Martin Meissner)

Sonia (surname witheld) embraces her children Mateo and Alessia at The Place de la Bourse as she pays her respects to victims following yesterday's terrorists attacks on March 23, 2016 in Brussels, Belgium. (Photo by Christopher Furlong/Getty Images)

People bring flowers and candles to Place de la Bourse, Brussels, to mourn for the victims on Wednesday evening, March 23, 2016. Bombs exploded Tuesday at the Brussels airport and one of the city's metro stations, killing and wounding scores of people, as a European capital was again locked down amid heightened security threats. (AP Photo/Martin Meissner)

A small girl sits among candles set up at a memorial site located at the old stock exchange in Brussels on Wednesday, March 23, 2016. Belgian authorities were searching Wednesday for a top suspect in the country's deadliest attacks in decades, as the European Union's capital awoke under guard and with limited public transport after scores were killed or wounded in bombings on the Brussels airport and a subway station. (AP Photo/Valentin Bianchi)

Hundreds of people come together at Place de la Bourse to mourn on Wednesday evening, March 23, 2016. Bombs exploded yesterday at the Brussels airport and one of the city's metro stations, killing and wounding scores of people, as a European capital was again locked down amid heightened security threats. (AP Photo/Martin Meissner)

People gather at a memorial site located at the old stock exchange in Brussels on Wednesday, March 23, 2016. Belgian authorities were searching Wednesday for a top suspect in the country's deadliest attacks in decades, as the European Union's capital awoke under guard and with limited public transport after scores were killed or wounded in bombings on the Brussels airport and a subway station. (AP Photo/Valentin Bianchi)

People bring flowers and candles at Place de la Bourse, Brussels, to mourn for the victims on Wednesday evening, March 23, 2016. Bombs exploded Tuesday at the Brussels airport and one of the city's metro stations, killing and wounding scores of people, as a European capital was again locked down amid heightened security threats. (AP Photo/Martin Meissner)

Candles and messages in front of the National Gallery in Trafalgar Square, London which is lit in the colours of the Belgium flag as a tribute following yesterday's terrorist attacks in Brussels. PRESS ASSOCIATION Photo. Picture date: Wednesday March 23, 2016. See PA story POLICE Brussels. Photo credit should read: Anthony Devlin/PA Wire

Messages written in chalk infront of the National Gallery in Trafalgar Square, London which is lit in the colours of the Belgium flag as a tribute following yesterday's terrorist attacks in Brussels. PRESS ASSOCIATION Photo. Picture date: Wednesday March 23, 2016. See PA story POLICE Brussels. Photo credit should read: Anthony Devlin/PA Wire

Candles and messages in front of the National Gallery in Trafalgar Square, London which is lit in the colours of the Belgium flag as a tribute following yesterday's terrorist attacks in Brussels. PRESS ASSOCIATION Photo. Picture date: Wednesday March 23, 2016. See PA story POLICE Brussels. Photo credit should read: Anthony Devlin/PA Wire

The National Gallery in Trafalgar Square, London are lit in the colours of the Belgium flag as a tribute following yesterday's terrorist attacks in Brussels. PRESS ASSOCIATION Photo. Picture date: Wednesday March 23, 2016. See PA story POLICE Brussels. Photo credit should read: Anthony Devlin/PA Wire

Messages written in chalk are seen in front of the National Gallery in Trafalgar Square, London which is lit in the colours of the Belgium flag as a tribute following yesterday's terrorist attacks in Brussels. PRESS ASSOCIATION Photo. Picture date: Wednesday March 23, 2016. See PA story POLICE Brussels. Photo credit should read: Anthony Devlin/PA Wire

The National Gallery in Trafalgar Square, London are lit in the colours of the Belgium flag as a tribute following yesterday's terrorist attacks in Brussels. PRESS ASSOCIATION Photo. Picture date: Wednesday March 23, 2016. See PA story POLICE Brussels. Photo credit should read: Anthony Devlin/PA Wire

Messages written in chalk infront of the National Gallery in Trafalgar Square, London which is lit in the colours of the Belgium flag as a tribute following yesterday's terrorist attacks in Brussels. PRESS ASSOCIATION Photo. Picture date: Wednesday March 23, 2016. See PA story POLICE Brussels. Photo credit should read: Anthony Devlin/PA Wire

The National Gallery in Trafalgar Square, London are lit in the colours of the Belgium flag as a tribute following yesterday's terrorist attacks in Brussels. PRESS ASSOCIATION Photo. Picture date: Wednesday March 23, 2016. See PA story POLICE Brussels. Photo credit should read: Anthony Devlin/PA Wire

The National Gallery in Trafalgar Square, London are lit in the colours of the Belgium flag as a tribute following yesterday's terrorist attacks in Brussels. PRESS ASSOCIATION Photo. Picture date: Wednesday March 23, 2016. See PA story POLICE Brussels. Photo credit should read: Anthony Devlin/PA Wire

The National Gallery in Trafalgar Square, London are lit in the colours of the Belgium flag as a tribute following yesterday's terrorist attacks in Brussels. PRESS ASSOCIATION Photo. Picture date: Wednesday March 23, 2016. See PA story POLICE Brussels. Photo credit should read: Anthony Devlin/PA Wire

London County Hall by the River Thames displays the colours of the Belgium Flag as a tribute following yesterday's terrorist attacks in Brussels. PRESS ASSOCIATION Photo. Picture date: Wednesday March 23, 2016. Photo credit should read: Ian West/PA Wire

The National Gallery and fountains in Trafalgar Square, London are lit in the colours of the Belgium flag as a tribute following yesterday's terrorist attacks in Brussels. PRESS ASSOCIATION Photo. Picture date: Wednesday March 23, 2016. See PA story POLICE Brussels. Photo credit should read: Anthony Devlin/PA Wire

The teams stand as a minute silence is observed for the victims of the Brussels attacks prior to the friendly football match between Romania and Lithuania in Bucharest March 23, 2016. Romania won 1-0. / AFP PHOTO / DANIEL MIHAILESCUDANIEL MIHAILESCU/AFP/Getty Images

The National Gallery in Trafalgar Square, London are lit in the colours of the Belgium flag as a tribute following yesterday's terrorist attacks in Brussels. PRESS ASSOCIATION Photo. Picture date: Wednesday March 23, 2016. See PA story POLICE Brussels. Photo credit should read: Anthony Devlin/PA Wire

BRUSSELS, BELGIUM - MARCH 23: A woman covers her face near Maelbeek metro station as she reacts following yesterday's attack, on March 23, 2016 in Brussels, Belgium. Belgium is observing three days of national mourning after 34 people were killed in a twin suicide blast at Zaventem Airport and a further bomb attack at Maelbeek Metro Station. Two brothers are thought to have carried out the airport attack and an international manhunt is underway for a third suspect. The attacks come just days after a key suspect in the Paris attacks, Salah Abdeslam, was captured in Brussels. (Photo by Carl Court/Getty Images) *** BESTPIX ***

A Belgian national flag is projected onto the National Gallery in Trafalgar Square, London, in solidarity with Belgium after the attacks that occurred yesterday in Brussels, Wednesday, March 23, 2016. Belgians began three days of mourning Wednesday for the victims of the Brussels airport and subway bombings, and the country remained on high alert as authorities hunted for one of the suspected attackers seen on surveillance video with two others who blew themselves up. (AP Photo/Matt Dunham)

BRUSSELS, BELGIUM - MARCH 23: A man wears the Belgian flag as people observe a one minute silence at the Place De La Bourse in honour of the victims of yesterdays' terror attacks on March 23, 2016 in Brussels, Belgium. Belgium is observing three days of national mourning after 34 people were killed in a twin suicide blast at Zaventem Airport and a further bomb attack at Maelbeek Metro Station. Two brothers are thought to have carried out the airport attack and an international manhunt is underway for a third suspect. The attacks come just days after a key suspect in the Paris attacks, Salah Abdeslam, was captured in Brussels. (Photo by Christopher Furlong/Getty Images) *** BESTPIX ***

LONDON, ENGLAND - MARCH 23: The arches of Wembley Stadium are illuminated with the colours of the flag of Belgium on March 23, 2016 in London, England. Belgium is observing three days of national mourning after 31 people were killed in a twin suicide blast at Zaventem Airport and a further bomb attack at Maelbeek Metro Station. Two brothers are thought to have carried out the airport attack and an international manhunt is underway for a third suspect. The attacks come just days after a key suspect in the Paris attacks, Salah Abdeslam, was captured in Brussels. (Photo by Ben Pruchnie/Getty Images)

A couple stand on March 23, 2016 in front of a makeshift memorial with floral tributes and candles in Brussels a day after triple bomb attacks at the Brussels airport and at a subway train station killed 31 people and wounded more than 200.
World leaders united in condemning the carnage in Brussels and vowed to combat terrorism, after Islamic State bombers attacked the symbolic heart of the EU. / AFP PHOTO / PHILIPPE HUGUENPHILIPPE HUGUEN/AFP/Getty Images

People light candles which create an heart shape at at a wake of Brussels Airport employees on Martch 23, 2016 in Zaventem, a day after triple bomb attacks at the Brussels airport and at a subway train station killed 31 people and wounded more than 200.
World leaders united in condemning the carnage in Brussels and vowed to combat terrorism, after Islamic State bombers attacked the symbolic heart of the EU. / AFP PHOTO / BELGA AND Belga / YORICK JANSENS / Belgium OUTYORICK JANSENS/AFP/Getty Images

Two children write on a wall at a memorial for victims of attacks in Brussels on Wednesday, March 23, 2016. Belgian authorities were searching Wednesday for a top suspect in the country's deadliest attacks in decades, as the European Union's capital awoke under guard and with limited public transport after scores were killed and injured in bombings on the Brussels airport and a subway station. (AP Photo/Valentin Bianchi)

Brussels airport workers and their relatives hold candles as they pay tribute to the victims of Brussels triple attacks near the airport in Zaventem on March 23, 2016, a day after triple bomb attacks at the Brussels airport and at a subway train station killed 31 people and wounded more than 200.
World leaders united in condemning the carnage in Brussels and vowed to combat terrorism, after Islamic State bombers attacked the symbolic heart of the EU. / AFP PHOTO / PHILIPPE HUGUENPHILIPPE HUGUEN/AFP/Getty Images

Brussels airport workers and their relatives place candles at a makeshift memorial as they pay tribute to the victims of Brussels triple attacks near the airport in Zaventem on March 23, 2016, a day after triple bomb attacks at the Brussels airport and at a subway train station killed 31 people and wounded more than 200.
World leaders united in condemning the carnage in Brussels and vowed to combat terrorism, after Islamic State bombers attacked the symbolic heart of the EU. / AFP PHOTO / PHILIPPE HUGUENPHILIPPE HUGUEN/AFP/Getty Images

Brussels airport workers and their relatives place candles as they pay tribute to the victims of Brussels triple attacks near the airport in Zaventem on March 23, 2016, a day after triple bomb attacks at the Brussels airport and at a subway train station killed 31 people and wounded more than 200.
World leaders united in condemning the carnage in Brussels and vowed to combat terrorism, after Islamic State bombers attacked the symbolic heart of the EU. / AFP PHOTO / PHILIPPE HUGUENPHILIPPE HUGUEN/AFP/Getty Images

Brussels airport workers and their relatives hold candles as they pay tribute to the victims of Brussels triple attacks near the airport in Zaventem on March 23, 2016, a day after triple bomb attacks at the Brussels airport and at a subway train station killed 31 people and wounded more than 200.
World leaders united in condemning the carnage in Brussels and vowed to combat terrorism, after Islamic State bombers attacked the symbolic heart of the EU. / AFP PHOTO / PHILIPPE HUGUENPHILIPPE HUGUEN/AFP/Getty Images

Brussels airport workers and their relatives react as they pay tribute to the victims of Brussels triple attacks near the airport in Zaventem on March 23, 2016, a day after triple bomb attacks at the Brussels airport and at a subway train station killed 31 people and wounded more than 200.
World leaders united in condemning the carnage in Brussels and vowed to combat terrorism, after Islamic State bombers attacked the symbolic heart of the EU. / AFP PHOTO / PHILIPPE HUGUENPHILIPPE HUGUEN/AFP/Getty Images

Brussels airport workers and their relatives hold candles as they pay tribute to the victims of Brussels triple attacks near the airport in Zaventem on March 23, 2016, a day after triple bomb attacks at the Brussels airport and at a subway train station killed 31 people and wounded more than 200.
World leaders united in condemning the carnage in Brussels and vowed to combat terrorism, after Islamic State bombers attacked the symbolic heart of the EU. / AFP PHOTO / PHILIPPE HUGUENPHILIPPE HUGUEN/AFP/Getty Images

Manchester Town Hall displays the colours of the Belgium Flag as a tribute following yesterday's terrorist attacks in Brussels. PA

Composite image showing Tower Bridge in central London lit in the colours of the Belgium flag as a tribute following yesterday's terrorist attacks in Brussels. PA

BRUSSELS, BELGIUM - MARCH 23: Paper butterflies and messages of support adorn the walls of the Bourse De Brussels building in the Place de la Bourse following yesterday's terrorists attacks on March 23, 2016 in Brussels, Belgium. Belgium is observing three days of national mourning after 34 people were killed in a twin suicide blast at Zaventem Airport and a further bomb attack at Maelbeek Metro Station. Two brothers are thought to have carried out the airport attack and an international manhunt is underway for a third suspect. The attacks come just days after a key suspect in the Paris attacks, Salah Abdeslam, was captured in Brussels. (Photo by Christopher Furlong/Getty Images)

BRUSSELS, BELGIUM - MARCH 23: Flowers, candles and tributes, to the victims and injured, continue to adorn the Place de la Bourse following yesterday's terrorists attacks on March 23, 2016 in Brussels, Belgium. Belgium is observing three days of national mourning after 34 people were killed in a twin suicide blast at Zaventem Airport and a further bomb attack at Maelbeek Metro Station. Two brothers are thought to have carried out the airport attack and an international manhunt is underway for a third suspect. The attacks come just days after a key suspect in the Paris attacks, Salah Abdeslam, was captured in Brussels. (Photo by Christopher Furlong/Getty Images)

Belgian flags reading "Pray for Belgium" are pictured as people gather at a makeshift memorial on the Place de la Bourse (Beursplein) in Brussels on March 23, 2016, a day after a triple bomb attack, which responsibility was claimed by the Islamic State group, left 31 dead and hundreds injured in the Belgian capital. World leaders united in condemning the carnage in Brussels and vowed to combat terrorism, after Islamic State bombers killed 31 people in a strike at the symbolic heart of the EU. AFP PHOTO / KENZO TRIBOUILLARDKENZO TRIBOUILLARD/AFP/Getty Images

A woman holds a placard with a heart-shaped Belgian flag reading "We want peace on Earth" as people gather at a makeshift memorial on the Place de la Bourse (Beursplein) in Brussels on March 23, 2016, a day after a triple bomb attack, which responsibility was claimed by the Islamic State group, left 31 dead and hundreds injured in the Belgian capital. World leaders united in condemning the carnage in Brussels and vowed to combat terrorism, after Islamic State bombers killed 31 people in a strike at the symbolic heart of the EU. AFP PHOTO / KENZO TRIBOUILLARDKENZO TRIBOUILLARD/AFP/Getty Images

People gather at a makeshift memorial on the Place de la Bourse (Beursplein) in Brussels on March 23, 2016, a day after a triple bomb attack, which responsibility was claimed by the Islamic State group, left 31 dead and hundreds injured in the Belgian capital. World leaders united in condemning the carnage in Brussels and vowed to combat terrorism, after Islamic State bombers killed 31 people in a strike at the symbolic heart of the EU. AFP PHOTO / KENZO TRIBOUILLARDKENZO TRIBOUILLARD/AFP/Getty Images

A woman hold a placard reading "Against terrorism and hatred, Solidarity" as people gather at a makeshift memorial on the Place de la Bourse (Beursplein) in Brussels on March 23, 2016, a day after a triple bomb attack, which responsibility was claimed by the Islamic State group, left 31 dead and hundreds injured in the Belgian capital. World leaders united in condemning the carnage in Brussels and vowed to combat terrorism, after Islamic State bombers killed 31 people in a strike at the symbolic heart of the EU. AFP PHOTO / KENZO TRIBOUILLARDKENZO TRIBOUILLARD/AFP/Getty Images

Flowers and candles are pictured as people gather at a makeshift memorial on the Place de la Bourse (Beursplein) in Brussels on March 23, 2016, a day after a triple bomb attack, which responsibility was claimed by the Islamic State group, left 31 dead and hundreds injured in the Belgian capital. World leaders united in condemning the carnage in Brussels and vowed to combat terrorism, after Islamic State bombers killed 31 people in a strike at the symbolic heart of the EU. AFP PHOTO / KENZO TRIBOUILLARDKENZO TRIBOUILLARD/AFP/Getty Images

Flowers and candles are pictured as people gather at a makeshift memorial on the Place de la Bourse (Beursplein) in Brussels on March 23, 2016, a day after a triple bomb attack, which responsibility was claimed by the Islamic State group, left 31 dead and hundreds injured in the Belgian capital. World leaders united in condemning the carnage in Brussels and vowed to combat terrorism, after Islamic State bombers killed 31 people in a strike at the symbolic heart of the EU. AFP PHOTO / KENZO TRIBOUILLARDKENZO TRIBOUILLARD/AFP/Getty Images

Flowers and candles are pictured as people gather at a makeshift memorial on the Place de la Bourse (Beursplein) in Brussels on March 23, 2016, a day after a triple bomb attack, which responsibility was claimed by the Islamic State group, left 31 dead and hundreds injured in the Belgian capital. World leaders united in condemning the carnage in Brussels and vowed to combat terrorism, after Islamic State bombers killed 31 people in a strike at the symbolic heart of the EU. AFP PHOTO / KENZO TRIBOUILLARDKENZO TRIBOUILLARD/AFP/Getty Images

People gather at a makeshift memorial on the Place de la Bourse (Beursplein) in Brussels on March 23, 2016, a day after a triple bomb attack, which responsibility was claimed by the Islamic State group, left 31 dead and hundreds injured in the Belgian capital. World leaders united in condemning the carnage in Brussels and vowed to combat terrorism, after Islamic State bombers killed 31 people in a strike at the symbolic heart of the EU. AFP PHOTO / KENZO TRIBOUILLARDKENZO TRIBOUILLARD/AFP/Getty Images

People gather at a makeshift memorial on the Place de la Bourse (Beursplein) in Brussels on March 23, 2016, a day after a triple bomb attack, which responsibility was claimed by the Islamic State group, left 31 dead and hundreds injured in the Belgian capital. World leaders united in condemning the carnage in Brussels and vowed to combat terrorism, after Islamic State bombers killed 31 people in a strike at the symbolic heart of the EU. AFP PHOTO / KENZO TRIBOUILLARDKENZO TRIBOUILLARD/AFP/Getty Images

King Philippe - Filip of Belgium and Queen Mathilde of Belgium mourn after laying down flowers in the area of the explosion at the Maelbeek - Maalbeek subway station in Brussels, on March 23, 2016, a day after the triple blasts killed some 30 people and left around 250 injured.
World leaders united in condemning the carnage in Brussels and vowed to combat terrorism, after Islamic State bombers attacked the symbolic heart of the EU. / AFP PHOTO / BELGA / THIERRY ROGE / Belgium OUTTHIERRY ROGE/AFP/Getty Images

A heavily armed police officer stands watch in front of Union Station in Washington, DC, March 23, 2016.
A dozen Americans were wounded in the Brussels attacks and a number unaccounted for, but no US nationals were known to have been among the 31 dead, the State Department said Wednesday. / AFP PHOTO / Jim WatsonJIM WATSON/AFP/Getty Images

TOPSHOT - A boy lights a candle at a makeshift memorial on the Place de la Bourse (Beursplein) in Brussels on March 23, 2016, a day after blasts hit the Belgian capital. World leaders united in condemning the carnage in Brussels and vowed to combat terrorism, after Islamic State bombers killed 31 people in a strike at the symbolic heart of the EU. AFP PHOTO / KENZO TRIBOUILLARD / AFP PHOTO / KENZO TRIBOUILLARDKENZO TRIBOUILLARD/AFP/Getty Images

Queen Mathilde of Belgium (C) meets soldiers during a visit to Brussels Airport, in Zaventem, on March 23, 2016, a day after triple bomb attacks at the Brussels airport and at a subway train station killed 31 people and wounded more than 200.
World leaders united in condemning the carnage in Brussels and vowed to combat terrorism, after Islamic State bombers attacked the symbolic heart of the EU. / AFP PHOTO / POOL / FREDERIC SIERAKOWSKIFREDERIC SIERAKOWSKI/AFP/Getty Images

A Belgian flag is pictured onto one of the two lion sculptures at a makeshift memorial on the Place de la Bourse (Beursplein) in Brussels on March 23, 2016, a day after blasts hit the Belgian capital. World leaders united in condemning the carnage in Brussels and vowed to combat terrorism, after Islamic State bombers killed 31 people in a strike at the symbolic heart of the EU. AFP PHOTO / KENZO TRIBOUILLARDKENZO TRIBOUILLARD/AFP/Getty Images

Candles and a printed message are pictured at a makeshift memorial on the Place de la Bourse (Beursplein) in Brussels on March 23, 2016, a day after blasts hit the Belgian capital. World leaders united in condemning the carnage in Brussels and vowed to combat terrorism, after Islamic State bombers killed 31 people in a strike at the symbolic heart of the EU. AFP PHOTO / KENZO TRIBOUILLARDKENZO TRIBOUILLARD/AFP/Getty Images

BRUSSELS, BELGIUM - MARCH 23: People chant and sing songs at the Place De La Bourse in honour of the victims of yesterdays' terror attacks on March 23, 2016 in Brussels, Belgium. Belgium is observing three days of national mourning after 34 people were killed in a twin suicide blast at Zaventem Airport and a further bomb attack at Maelbeek Metro Station. Two brothers are thought to have carried out the airport attack and an international manhunt is underway for a third suspect. The attacks come just days after a key suspect in the Paris attacks, Salah Abdeslam, was captured in Brussels. (Photo by Christopher Furlong/Getty Images)

BRUSSELS, BELGIUM - MARCH 23: A soldier checks the identification of a person entering Brussels Midi train station on March 23, 2016 in Brussels, Belgium. Belgium is observing three days of national mourning after 34 people were killed in a twin suicide blast at Zaventem Airport and a further bomb attack at Maelbeek Metro Station. Two brothers are thought to have carried out the airport attack and an international manhunt is underway for a third suspect. The attacks come just days after a key suspect in the Paris attacks, Salah Abdeslam, was captured in Brussels. (Photo by Carl Court/Getty Images)

A man pays tribute to the victims of the Brussels attacks next to a Tunisian flag at a makeshift memorial on the Place de la Bourse - Beursplein square in Brussels, on March 23, 2016, a day after triple bomb attacks at the Brussels airport and at a subway train station killed 31 people and wounded more than 200.
World leaders united in condemning the carnage in Brussels and vowed to combat terrorism, after Islamic State bombers attacked the symbolic heart of the EU. / AFP PHOTO / BELGA / AURORE BELOT / Belgium OUTAURORE BELOT/AFP/Getty Images

People gather to pay tribute to the victims of the Brussels attacks on the Place de la Bourse in central Brussels, on March 23, 2016, a day after the triple blasts killed some 30 people and left around 250 injured.
World leaders united in condemning the carnage in Brussels and vowed to combat terrorism, after Islamic State bombers attacked the symbolic heart of the EU. / AFP PHOTO / Belga / AURORE BELOT / Belgium OUTAURORE BELOT/AFP/Getty Images

Photos shows colours of the Belgian flag being projected on to (from top L) the Brandenburg Gate in Berlin, the Eiffel Tower in Paris, the town council building in Belgrade, the Trevi Fountain in Rome, the Royal Palace at Dam Square in Amsterdam and Rome's Campidoglio in tribute to the victims of the Brussels attacks. AFP/Getty Images

TOPSHOT - Belgian police officers stand guard near Maelbeek - Maalbeek subway station in Brussels on March 23, 2016, a day after triple bomb attacks in the Belgian capital killed about 35 people and left more than 200 people wounded. A series of explosions claimed by the Islamic State group ripped through Brussels airport and a metro train on March 22, killing around 35 people in the latest attacks to bring bloody carnage to the heart of Europe. AFP PHOTO / KENZO TRIBOUILLARD / AFP PHOTO / KENZO TRIBOUILLARDKENZO TRIBOUILLARD/AFP/Getty Images

BRUSSELS, BELGIUM - MARCH 23: A sad face is drawn on a Belgian flag near Maelbeek metro station following yesterday's attack, on March 23, 2016 in Brussels, Belgium. Belgium is observing three days of national mourning after 34 people were killed in a twin suicide blast at Zaventem Airport and a further bomb attack at Maelbeek Metro Station. Two brothers are thought to have carried out the airport attack and an international manhunt is underway for a third suspect. The attacks come just days after a key suspect in the Paris attacks, Salah Abdeslam, was captured in Brussels. (Photo by Carl Court/Getty Images)

Photos issued by the Belgian Federal Police of Najim Laachraoui, who according to local media is thought to be connected with the Brussels attacks, and who is believed to be on the run. Belgian Federal Police/PA Wire

Belgian federal police released this image of Brussels bomb suspects. The two men on the left, each wearing a single black glove, are thought to be suicide bombers, while the third is thought to be on the run.

A picture taken on March 22, 2016 shows Red Cross tents and police vehicles at the Wetstraat - Rue de la Loi, which was evacuated after an explosion at the Maelbeek - Maalbeek subway station in Brussels. A series of explosions claimed by the Islamic State group ripped through Brussels airport and a metro train Tuesday, killing around 35 people in the latest attacks to bring bloody carnage to the heart of Europe. / AFP PHOTO / Belga / LAURIE DIEFFEMBACQ / Belgium OUTLAURIE DIEFFEMBACQ/AFP/Getty Images

A woman lights a candle among floral tributes, a cross and notes in front of the Bourse of Brussels on March 22, 2016 in tribute to the victims of Brussels following triple bomb attacks in the Belgian capital that killed about 35 people and left more than 200 people wounded. Belgium launched a huge manhunt on March 22 after a series of bombings claimed by the Islamic State group ripped through Brussels airport and a metro train, killing around 35 people in the latest attack to bring carnage to the heart of Europe.
/ AFP PHOTO / BELGA AND Belga / Aurore Belot / Belgium OUTAURORE BELOT/AFP/Getty Images

A woman lights a candle among floral tributes and notes in front of the Bourse of Brussels on March 22, 2016 in tribute to the victims of Brussels following triple bomb attacks in the Belgian capital that killed about 35 people and left more than 200 people wounded. AFP/Getty Images

People hold a banner reading in French and Flamish "I AM BRUSSELS" as they gather around floral tributes, candles, belgian and peace flags and notes in front of the Bourse of Brussels on March 22, 2016. AFP/Getty Images

A picture taken on March 22, 2016 shows the Belgian flag projected on the European Union Commisson building in tribute to the victims of Brussels following triple bomb attacks in the Belgian capital that killed about 35 people and left more than 200 people wounded.
Belgium launched a huge manhunt on March 22 after a series of bombings claimed by the Islamic State group ripped through Brussels airport and a metro train, killing around 35 people in the latest attack to bring carnage to the heart of Europe. / AFP PHOTO / PHILIPPE HUGUENPHILIPPE HUGUEN/AFP/Getty Images

People hold a banner reading in French and Flamish "I AM BRUSSELS" as they gather around floral tributes, candles, belgian flags and notes in front of the Bourse of Brussels on March 22, 2016 in tribute to the victims of Brussels following triple bomb attacks in the Belgian capital that killed about 35 people and left more than 200 people wounded. Belgium launched a huge manhunt on March 22 after a series of bombings claimed by the Islamic State group ripped through Brussels airport and a metro train, killing around 35 people in the latest attack to bring carnage to the heart of Europe.
/ AFP PHOTO / BELGA AND Belga / Aurore Belot / Belgium OUTAURORE BELOT/AFP/Getty Images

People light candles at the Place de la Bourse following today's attacks on March 22, 2016 in Brussels, Belgium. (Photo by Carl Court/Getty Images)

LOS ANGELES, CA - MARCH 22: Los Angeles County Sheriffs deputies patrol Union Station train hub as security is heightened in reaction to bomb attacks in Brussels, Belgium this morning on March 22, 2016 in Los Angeles, California. At least 36 lives and injured at least 200 people in the morning rush hour bomb attacks at the international airport and a subway station. (Photo by David McNew/Getty Images)

BRUSSELS, BELGIUM - MARCH 22: A person writes a message as people leave tributes at the Place de la Bourse following today's attacks on March 22, 2016 in Brussels, Belgium. At least 31 people are thought to have been killed after Brussels airport and a Metro station were targeted by explosions. The attacks come just days after a key suspect in the Paris attacks, Salah Abdeslam, was captured in Brussels. (Photo by Carl Court/Getty Images)

The Eiffel Tower is illuminated with the Belgium national colors black, yellow and red in honor of the victims of the today's attacks at the airport and the metro station in Brussels, in Paris, Tuesday, March 22, 2016. (AP Photo/Thibault Camus)

The Belgian flag is projected on Rome's historical Trevi Fountain to honor the victims of the deadly attacks at Brussels airport and subway, Tuesday, March 22, 2016. (AP Photo/Andrew Medichini)

LOS ANGELES, CA - MARCH 22: A Los Angeles County Sheriffs deputy patrols Union Station train hub as security is heightened in reaction to bomb attacks in Brussels, Belgium this morning on March 22, 2016 in Los Angeles, California. At least 36 lives and injured at least 200 people in the morning rush hour bomb attacks at the international airport and a subway station. (Photo by David McNew/Getty Images)

A writing on the asphalt reads "Brussels forever" at the place de la Bourse in the center of Brussels, where people write hundreds of messages on the ground to remember the victims of todays attack, Tuesday, March 22, 2016. Bombs exploded at the Brussels airport and one of the city's metro stations Tuesday, killing and wounding scores of people, as a European capital was again locked down amid heightened security threats. (AP Photo/Martin Meissner)

Two Belgian flags are projected on Rome's Campidoglio Capitol Hill to honor the victims of the deadly attacks at Brussels airport and subway, Tuesday, March 22, 2016. Explosions, at least one likely caused by a suicide bomber, rocked the Brussels airport and its subway system prompting a lockdown of the Belgian capital and heightened security across Europe. (AP Photo/Andrew Medichini)

People light candles at a makeshift memorial at Place de la Bourse (Beursplein) following attacks in Brussels on March 22, 2016. A series of explosions claimed by the Islamic State group ripped through Brussels airport and a metro train on March 22, killing around 35 people in the latest attacks to bring bloody carnage to the heart of Europe. AFP PHOTO / THIERRY MONASSETHIERRY MONASSE/AFP/Getty Images

People gather at a makeshift memorial at Place de la Bourse (Beursplein) following attacks in Brussels on March 22, 2016. AFP/Getty Images

People light candles in the shape of a heart outside the stock exchange in Brussels on Tuesday, March 22, 2016. Explosions, at least one likely caused by a suicide bomber, rocked the Brussels airport and subway system Tuesday, prompting a lockdown of the Belgian capital and heightened security across Europe. (AP Photo/Geert Vanden Wijngaert)

People bring flowers and candles to mourn at the Place de la Bourse in the center of Brussels, Tuesday, March 22, 2016. Bombs exploded at the Brussels airport and one of the city's metro stations Tuesday, killing and wounding scores of people, as a European capital was again locked down amid heightened security threats. (AP Photo/Martin Meissner)

A picture taken on March 22, 2016 shows the Royal Palace at Dam Square in Amsterdam displaying the colors of the Belgian flag in tribute to the victims of Brussels following triple bomb attacks in the Belgian capital that killed about 35 people and left more than 200 people wounded. Belgium launched a huge manhunt on March 22 after a series of bombings claimed by the Islamic State group ripped through Brussels airport and a metro train, killing around 35 people in the latest attack to bring carnage to the heart of Europe. / AFP PHOTO / ANP / Evert Elzinga / Netherlands OUTEVERT ELZINGA/AFP/Getty Images

A photo taken on March 22, 2016 shows the Belgian flag projected on Rome's Campidoglio in tribute to the victims of Brussels following triple bomb attacks in the Belgian capital that killed about 35 people and left more than 200 people wounded. Belgium launched a huge manhunt on March 22 after a series of bombings claimed by the Islamic State group ripped through Brussels airport and a metro train, killing around 35 people in the latest attack to bring carnage to the heart of Europe. / AFP PHOTO / FILIPPO MONTEFORTEFILIPPO MONTEFORTE/AFP/Getty Images

A candle is lit at a makeshift memorial in front of the stock exchange at the Place de la Bourse (Beursplein) in Brussels on March 22, 2016, following triple bomb attacks in the Belgian capital that killed about 35 people and left more than 200 people wounded. A series of explosions claimed by the Islamic State group ripped through Brussels airport and a metro train on March 22, killing around 35 people in the latest attacks to bring bloody carnage to the heart of Europe. AFP PHOTO / KENZO TRIBOUILLARDKENZO TRIBOUILLARD/AFP/Getty Images

BRUSSELS, BELGIUM - MARCH 22: People gather to leave tributes at the Place de la Bourse following today's attacks on March 22, 2016 in Brussels, Belgium. At least 31 people are thought to have been killed after Brussels airport and a Metro station were targeted by explosions. The attacks come just days after a key suspect in the Paris attacks, Salah Abdeslam, was captured in Brussels. (Photo by Carl Court/Getty Images) *** BESTPIX ***

BRUSSELS, BELGIUM - MARCH 22: A young girl lights a candle at the Place de la Bourse following today's attacks on March 22, 2016 in Brussels, Belgium. At least 31 people are thought to have been killed after Brussels airport and a Metro station were targeted by explosions. The attacks come just days after a key suspect in the Paris attacks, Salah Abdeslam, was captured in Brussels. (Photo by Carl Court/Getty Images) *** BESTPIX ***

BRUSSELS, BELGIUM - MARCH 22: Passengers are evacuated from Zaventem Bruxelles International Airport after a terrorist attack on March 22, 2016 in Brussels, Belgium. At least 13 people are though to have been killed after Brussels airport was hit by two explosions whilst a Metro station was also targeted. The attacks come just days after a key suspect in the Paris attacks, Salah Abdeslam, was captured in Brussels. (Photo by Sylvain Lefevre/Getty Images) *** BESTPIX ***

WASHINGTON, DC - MARCH 22: An Amtrak police K-9 unit patrols Union Station March 22, 2016 in Washington, DC. Security has been increased around the city after bombings in Brussels have left at least 34 people dead and scores more injured in the bombings. (Photo by Win McNamee/Getty Images) *** BESTPIX ***

A woman reacts at a makeshift memorial in front of the stock exchange at the Place de la Bourse (Beursplein) in Brussels on March 22, 2016, following triple bomb attacks in the Belgian capital that killed about 35 people and left more than 200 people wounded. A series of explosions claimed by the Islamic State group ripped through Brussels airport and a metro train on March 22, killing around 35 people in the latest attacks to bring bloody carnage to the heart of Europe. AFP PHOTO / KENZO TRIBOUILLARDKENZO TRIBOUILLARD/AFP/Getty Images

Young women hold each other at a makeshift memorial in front of the stock exchange at the Place de la Bourse (Beursplein) in Brussels on March 22, 2016, following triple bomb attacks in the Belgian capital that killed about 35 people and left more than 200 people wounded. A series of explosions claimed by the Islamic State group ripped through Brussels airport and a metro train on March 22, killing around 35 people in the latest attacks to bring bloody carnage to the heart of Europe. AFP PHOTO / KENZO TRIBOUILLARDKENZO TRIBOUILLARD/AFP/Getty Images

Messages and tributes left by members of the public at the Place de la Bourse in Brussels following the terrorist bomb attacks. PRESS ASSOCIATION Photo. Picture date: Tuesday March 22, 2016. The attacks, condemned as "blind, violent and cowardly" by Belgian Prime Minister Charles Michel, came after the arrest in the city last week of terror mastermind Salah Abdeslam, who plotted November's Paris atrocity from the notorious Molenbeek suburb of Brussels. See PA story POLICE Brussels. Photo credit should read: Gareth Fuller/PA Wire

A Belgian flag is display on the Trevi Fountain in Rome on March 22, 2016 in tribute to the victims of Brussels following triple bomb attacks in the Belgian capital that killed about 35 people and left more than 200 people wounded. Belgium launched a huge manhunt on March 22 after a series of bombings claimed by the Islamic State group ripped through Brussels airport and a metro train, killing around 35 people in the latest attack to bring carnage to the heart of Europe. / AFP PHOTO / GABRIEL BOUYSGABRIEL BOUYS/AFP/Getty Images

A Federal police helicopter shines light on roofs during searchings at the Place Princesse Elisabeth in Schaarbeek in the region of Brussels on March 22, 2016, during ongoing security operations in the wake of triple bomb attacks in the Belgian capital that killed about 35 people and left more than 200 people wounded. A series of explosions claimed by the Islamic State group ripped through Brussels airport and a metro train on March 22, killing around 35 people in the latest attacks to bring bloody carnage to the heart of Europe. / AFP PHOTO / Belga / James Arthur Gekiere / Belgium OUTJAMES ARTHUR GEKIERE/AFP/Getty Images

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Handout CCTV image issued by Belgian Federal Police of three men they believed are connected with the explosions at Brussels airport. PRESS ASSOCIATION Photo. Picture date: Tuesday March 22, 2016. See PA story POLICE Brussels. Photo credit should read: Belgian Federal Police/PA Wire
NOTE TO EDITORS: This handout photo may only be used in for editorial reporting purposes for the contemporaneous illustration of events, things or the people in the image or facts mentioned in the caption. Reuse of the picture may require further permission from the copyright holder.

A member of the public holds a Belgium and Palestine flag at the Place de la Bourse in Brussels following the terrorist bomb attacks. PRESS ASSOCIATION Photo. Picture date: Tuesday March 22, 2016. The attacks, condemned as "blind, violent and cowardly" by Belgian Prime Minister Charles Michel, came after the arrest in the city last week of terror mastermind Salah Abdeslam, who plotted November's Paris atrocity from the notorious Molenbeek suburb of Brussels. See PA story POLICE Brussels. Photo credit should read: Gareth Fuller/PA Wire

BRUSSELS, BELGIUM - MARCH 22: A man waves a Belgian and Palestinian flag as a mark of solidarity at the Place de la Bourse following today's attacks on March 22, 2016 in Brussels, Belgium. At least 31 people are thought to have been killed after Brussels airport and a Metro station were targeted by explosions. The attacks come just days after a key suspect in the Paris attacks, Salah Abdeslam, was captured in Brussels. (Photo by Carl Court/Getty Images)

A woman holds a drawing by French cartoonist Plantu picturing a character made of a French flag consoling another made of the Belgian flag, in front of the Hotel de Ville in Paris as people gather for a tribute to the victims of Brussels following triple bomb attacks in the Belgian capital that killed about 35 people and left more than 200 people wounded. Belgium launched a huge manhunt on March 22 after a series of bombings claimed by the Islamic State group ripped through Brussels airport and a metro train, killing around 35 people in the latest attack to bring carnage to the heart of Europe. / AFP PHOTO / MARTIN BUREAUMARTIN BUREAU/AFP/Getty Images

Police officers patrol outside the Maelbeek - Maalbeek subway station in Brussels on March 22, 2016, following a series of attacks in Brussels today claimed by the Islamic State group killing at least 35 people were killed and more than 200 wounded. / AFP PHOTO / PHILIPPE HUGUENPHILIPPE HUGUEN/AFP/Getty Images

A couple watches as the colors of the Belgian flag are projected on to the Brandenburg Gate in Berlin as the German capital shows its solidarity following the Brussels attacks on March 22, 2016.
Security was tightened across Europe and transport links paralysed after a series of apparently coordinated explosions ripped through Brussels airport and a metro train, killing at least 34 people. / AFP PHOTO / ODD ANDERSENODD ANDERSEN/AFP/Getty Images

A miniature sculpture of Brussels' landmark Manneken Pis (Little man Pee) is seen in tribute to victims at a makeshift memorial in front of the stock exchange at the Place de la Bourse (Beursplein) in Brussels on March 22, 2016, following triple bomb attacks in the Belgian capital that killed about 35 people and left more than 200 people wounded. A series of explosions claimed by the Islamic State group ripped through Brussels airport and a metro train on March 22, killing around 35 people in the latest attacks to bring bloody carnage to the heart of Europe. AFP PHOTO / KENZO TRIBOUILLARDKENZO TRIBOUILLARD/AFP/Getty Images

People stand hand in hand in tribute to victims at a makeshift memorial in front of the stock exchange at the Place de la Bourse (Beursplein) in Brussels on March 22, 2016, following triple bomb attacks in the Belgian capital that killed about 35 people and left more than 200 people wounded. A series of explosions claimed by the Islamic State group ripped through Brussels airport and a metro train on March 22, killing around 35 people in the latest attacks to bring bloody carnage to the heart of Europe.KENZO TRIBOUILLARD/AFP/Getty Images

A picture taken on March 22, 2016 shows a frame with an inscription which translates as "For our Belgian friends" among floral tributes, candles and notes at the Place de la Republique in Paris in tribute to the victims following a series of apparently coordinated explosions that ripped through Brussels airport and the metro train, killing at least 14 people in the airport and 20 people in the metro in the latest attacks to target Europe.
Belgian police found a bomb and an Islamic State flag during a search of a Brussels apartment carried out hours after deadly attacks in the Belgian capital that killed around 35 people, prosecutors said. The Islamic State group officially claimed responsibility for the attacks.
/ AFP PHOTO / JOEL SAGETJOEL SAGET/AFP/Getty Images

A woman lights a candle in tribute to victims at a makeshift memorial in front of the stock exchange at the Place de la Bourse (Beursplein) in Brussels on March 22, 2016, following triple bomb attacks in the Belgian capital that killed about 35 people and left more than 200 people wounded. A series of explosions claimed by the Islamic State group ripped through Brussels airport and a metro train on March 22, killing around 35 people in the latest attacks to bring bloody carnage to the heart of Europe. AFP PHOTO / THIERRY MONASSETHIERRY MONASSE/AFP/Getty Images

People stand hand in hand in tribute to victims at a makeshift memorial in front of the stock exchange at the Place de la Bourse (Beursplein) in Brussels on March 22, 2016, following triple bomb attacks in the Belgian capital that killed about 35 people and left more than 200 people wounded. A series of explosions claimed by the Islamic State group ripped through Brussels airport and a metro train on March 22, killing around 35 people in the latest attacks to bring bloody carnage to the heart of Europe. AFP PHOTO / THIERRY MONASSETHIERRY MONASSE/AFP/Getty Images

A man holds a sign as people take part in a rally on March 22, 2016 on the Palazzo di Citta square in Turin in memory of the victims of the attacks in Brussels. Around 35 people were killed and more than 200 wounded in a series of attacks in Brussels today claimed by the Islamic State group and described as a strike at the very heart of Europe. / AFP PHOTO / MARCO BERTORELLOMARCO BERTORELLO/AFP/Getty Images

Police officers stand guard at the Brussels Airport in Zaventem following twin blasts on March 22, 2016. Around 35 people were killed and more than 200 wounded in a series of attacks in Brussels today claimed by the Islamic State group and described as a strike at the very heart of Europe. / AFP PHOTO / PATRIK STOLLARZPATRIK STOLLARZ/AFP/Getty Images

BRUSSELS, BELGIUM - MARCH 22: A message is written on a wall following today's attacks on March 22, 2016 in Brussels, Belgium. At least 31 people are thought to have been killed after Brussels airport and a Metro station were targeted by explosions. The attacks come just days after a key suspect in the Paris attacks, Salah Abdeslam, was captured in Brussels. (Photo by Carl Court/Getty Images)

People take part in a rally on March 22, 2016 on the Palazzo di Citta square in Turin in memory of the victims of the attacks in Brussels. Around 35 people were killed and more than 200 wounded in a series of attacks in Brussels today claimed by the Islamic State group and described as a strike at the very heart of Europe. / AFP PHOTO / MARCO BERTORELLOMARCO BERTORELLO/AFP/Getty Images

BRUSSELS, BELGIUM - MARCH 22: A Metro station is closed off at the Place de la Bourse following today's attacks on March 22, 2016 in Brussels, Belgium. At least 31 people are thought to have been killed after Brussels airport and a Metro station were targeted by explosions. The attacks come just days after a key suspect in the Paris attacks, Salah Abdeslam, was captured in Brussels. (Photo by Carl Court/Getty Images)

People look at informations inside the North station (Gare du Nord - Noordstation) on March 22, 2016 in Brussels, as stations are opened again with high security measures after a series of apparently coordinated explosions that ripped through Brussels airport and the metro train, killing at least 14 people in the airport and 20 people in the metro in the latest attacks to target Europe.
Belgian police issued a wanted notice for a suspect in the bomb attack on Brussels airport on March 22 in which at least 14 people were killed. The Islamic State group officially claimed responsibility for the attacks in Brussels that left some 35 people dead and threatened further violence.
/ AFP PHOTO / Belga / NICOLAS MAETERLINCK / Belgium OUTNICOLAS MAETERLINCK/AFP/Getty Images

BRUSSELS, BELGIUM - MARCH 22: A woman writes a message on the ground as people leave tributes at the Place de la Bourse following today's attacks on March 22, 2016 in Brussels, Belgium. At least 31 people are thought to have been killed after Brussels airport and a Metro station were targeted by explosions. The attacks come just days after a key suspect in the Paris attacks, Salah Abdeslam, was captured in Brussels. (Photo by Carl Court/Getty Images)

People holds a banner as they gather at a makeshift memorial at Place de la Bourse (Beursplein) following attacks in Brussels on March 22, 2016. A series of explosions claimed by the Islamic State group ripped through Brussels airport and a metro train on March 22, killing around 35 people in the latest attacks to bring bloody carnage to the heart of Europe. THIERRY MONASSE AFP PHOTO / THIERRY MONASSETHIERRY MONASSE/AFP/Getty Images

Servicemen of Azov, Ukrainian volonteers battalion, hold torches in front of floral tributes during a ceremony in front of the Belgian embassy in Kiev on March 22, 2016, in tribute to the victims of Brussels following triple bomb attacks in the Belgian capital that killed about 35 people and left more than 200 people wounded. Belgium launched a huge manhunt on March 22 after a series of bombings claimed by the Islamic State group ripped through Brussels airport and a metro train, killing around 35 people in the latest attack to bring carnage to the heart of Europe. / AFP PHOTO / ANATOLII STEPANOVANATOLII STEPANOV/AFP/Getty Images

Belgian special police forces take position in Zaventem following blasts at Brussels airport and a metro station on March 22, 2016. The European Union vowed to defend democracy and tolerance and to combat terrorism "with all necessary means" after triple blasts struck Brussels, the 28-nation bloc's capital. Around 35 people were killed and more than 200 injured. The Islamic State jihadist group claimed responsibility. AFP PHOTO / JOHN THYSJOHN THYS/AFP/Getty Images

WASHINGTON, DC - MARCH 22: A K-9 unit patrols Union Station March 22, 2016 in Washington, DC. Security has been increased around the city after bombings in Brussels have left at least 34 people dead and scores more injured in the bombings. (Photo by Win McNamee/Getty Images)

WASHINGTON, DC - MARCH 22: An Amtrak police K-9 unit patrols Union Station March 22, 2016 in Washington, DC. Security has been increased around the city after bombings in Brussels have left at least 34 people dead and scores more injured in the bombings. (Photo by Win McNamee/Getty Images)

WASHINGTON, DC - MARCH 22: An Amtrak police K-9 unit checks the baggage of passengers at Union Station March 22, 2016 in Washington, DC. Security has been increased around the city after bombings in Brussels have left at least 34 people dead and scores more injured in the bombings. (Photo by Win McNamee/Getty Images)

BRUSSELS, BELGIUM - MARCH 22: A message is written on the ground as people leave tributes at the Place de la Bourse following today's attacks on March 22, 2016 in Brussels, Belgium. At least 31 people are thought to have been killed after Brussels airport and a Metro station were targeted by explosions. The attacks come just days after a key suspect in the Paris attacks, Salah Abdeslam, was captured in Brussels. (Photo by Carl Court/Getty Images)

Belgian flag flies at half mast above the Royal Palace in Brussels on March 22, 2016 in the wake of co-ordinated attacks claimed by Islamic State group (IS) millitants at the city's airport and in a Metro train. Belgium will hold three days of national mourning in the wake of the deadly attacks in the capital Brussels that killed around 35 people. "All national flags on public buildings will be at half-mast," Frederic Cauderlier, spokesman for Belgian premier Charles Michel, told AFP.
/ AFP PHOTO / BELGA AND Belga / NICOLAS MAETERLINCK / Belgium OUTNICOLAS MAETERLINCK/AFP/Getty Images

People gather at a makeshift memorial at Place de la Bourse (Beursplein) following attacks in Brussels on March 22, 2016. Airlines cancelled hundreds of flights and European railways froze links with Brussels after a series of bomb blasts killed around 35 people in the city's airport and a metro train, sparking a broad security response. AFP PHOTO / KENZO TRIBOUILLARDKENZO TRIBOUILLARD/AFP/Getty Images

BRUSSELS, BELGIUM - MARCH 22: A young boy helps light a candle as people leave tributes at the Place de la Bourse following today's attacks on March 22, 2016 in Brussels, Belgium. At least 31 people are thought to have been killed after Brussels airport and a Metro station were targeted by explosions. The attacks come just days after a key suspect in the Paris attacks, Salah Abdeslam, was captured in Brussels. (Photo by Carl Court/Getty Images)

BRUSSELS, BELGIUM - MARCH 22: A young boy helps light a candle as people leave tributes at the Place de la Bourse following today's attacks on March 22, 2016 in Brussels, Belgium. At least 31 people are thought to have been killed after Brussels airport and a Metro station were targeted by explosions. The attacks come just days after a key suspect in the Paris attacks, Salah Abdeslam, was captured in Brussels. (Photo by Carl Court/Getty Images)

BRUSSELS, BELGIUM - MARCH 22: People leave tributes at the Place de la Bourse following today's attacks on March 22, 2016 in Brussels, Belgium. At least 31 people are thought to have been killed after Brussels airport and a Metro station were targeted by explosions. The attacks come just days after a key suspect in the Paris attacks, Salah Abdeslam, was captured in Brussels. (Photo by Carl Court/Getty Images)

A man reacts as people gather at a makeshift memorial at Place de la Bourse (Beursplein) following attacks in Brussels on March 22, 2016. Airlines cancelled hundreds of flights and European railways froze links with Brussels after a series of bomb blasts killed around 35 people in the city's airport and a metro train, sparking a broad security response. AFP PHOTO / KENZO TRIBOUILLARDKENZO TRIBOUILLARD/AFP/Getty Images

Police forces block the access to the Maalbeek subway station, in Brussels, on March 22, 2016, after a series of apparently coordinated explosions that ripped through Brussels airport and the metro train, killing at least 14 people in the airport and 20 people in the metro in the latest attacks to target Europe. / AFP PHOTO / PHILIPPE HUGUENPHILIPPE HUGUEN/AFP/Getty Images

People hold hands as they gather at a makeshift memorial at Place de la Bourse (Beursplein) following attacks in Brussels on March 22, 2016. Airlines cancelled hundreds of flights and European railways froze links with Brussels after a series of bomb blasts killed around 35 people in the city's airport and a metro train, sparking a broad security response. AFP PHOTO / KENZO TRIBOUILLARDKENZO TRIBOUILLARD/AFP/Getty Images

A picture taken on March 22, 2016 in Paris shows a view of a smartphone screening an Instagram page with the ashtag "#JESUISBRUSSELS" (#IAMBRUSSELS) and two tributes images picturing the color of the Belgian flag, a drawing by French cartoonist Plantu and the famous Belgian comic character Tintin, in tribute to victims of triple bomb attacks in the Belgian capital that killed about 35 people. Airlines cancelled hundreds of flights and European railways froze links with Brussels on March 22, 2016 after rush-hour bomb attacks killed around 35 people in the city's airport and a metro train, sparking a broad security response. Within hours of Brussels attacks tens of thousands of people were sharing images on social media of Herge's cub reporter Tintin, the country's most famous creation, in tears.
/ AFP PHOTO / JOEL SAGET / RESTRICTED TO EDITORIAL USE - MANDATORY MENTION OF THE ARTIST UPON PUBLICATION - TO ILLUSTRATE THE EVENT AS SPECIFIED IN THE CAPTIONJOEL SAGET/AFP/Getty Images

A replica of the Manneken Pis statue stands at a makeshift memorial at Place de la Bourse (Beursplein) following attacks in Brussels on March 22, 2016. Airlines cancelled hundreds of flights and European railways froze links with Brussels after a series of bomb blasts killed around 35 people in the city's airport and a metro train, sparking a broad security response. AFP PHOTO / KENZO TRIBOUILLARDKENZO TRIBOUILLARD/AFP/Getty Images

A man plays the cello as people gather at a makeshift memorial at Place de la Bourse (Beursplein) following attacks in Brussels on March 22, 2016. Airlines cancelled hundreds of flights and European railways froze links with Brussels after a series of bomb blasts killed around 35 people in the city's airport and a metro train, sparking a broad security response. AFP PHOTO / KENZO TRIBOUILLARDKENZO TRIBOUILLARD/AFP/Getty Images

People hold hands as they gather at a makeshift memorial at Place de la Bourse (Beursplein) following attacks in Brussels on March 22, 2016. Airlines cancelled hundreds of flights and European railways froze links with Brussels after a series of bomb blasts killed around 35 people in the city's airport and a metro train, sparking a broad security response. AFP PHOTO / KENZO TRIBOUILLARDKENZO TRIBOUILLARD/AFP/Getty Images

People hold hands as they gather at a makeshift memorial at Place de la Bourse (Beursplein) following attacks in Brussels on March 22, 2016. Airlines cancelled hundreds of flights and European railways froze links with Brussels after a series of bomb blasts killed around 35 people in the city's airport and a metro train, sparking a broad security response. AFP PHOTO / KENZO TRIBOUILLARDKENZO TRIBOUILLARD/AFP/Getty Images

A Belgian police officer watches people walk past during an operation to limit the number of people allowed into the central Station in Brussels on March 22, 2016 following co-ordinated attacks at the Airport serving the Belgian capital and its Metro system. Airlines cancelled hundreds of flights and European railways froze links with Brussels after a series of bombs blasts killed around 35 people in the city's airport and a metro train, sparking a broad security response. / AFP PHOTO / EMMANUEL DUNANDEMMANUEL DUNAND/AFP/Getty Images

A woman reacts as people gather at a makeshift memorial at Place de la Bourse (Beursplein) following attacks in Brussels on March 22, 2016. Airlines cancelled hundreds of flights and European railways froze links with Brussels after a series of bomb blasts killed around 35 people in the city's airport and a metro train, sparking a broad security response. AFP PHOTO / KENZO TRIBOUILLARDKENZO TRIBOUILLARD/AFP/Getty Images

A woman lights a candle at a makeshift memorial at Place de la Bourse (Beursplein) following attacks in Brussels on March 22, 2016. Airlines cancelled hundreds of flights and European railways froze links with Brussels after a series of bomb blasts killed around 35 people in the city's airport and a metro train, sparking a broad security response. AFP PHOTO / KENZO TRIBOUILLARDKENZO TRIBOUILLARD/AFP/Getty Images

A woman leaves a bouquet of flowers in the Belgian national colours next to a French national flag with the lettering 'Paris - Brussels - Solidarity' at the fence of the Belgian embassy in Paris on March 22, 2016, in tribute to victims of triple bomb attacks in the Belgian capital that killed about 35 people. AFP PHOTO / THOMAS SAMSONTHOMAS SAMSON/AFP/Getty Images

A candle burns next to a heart drawing at a makeshift memorial at Place de la Bourse (Beursplein) following attacks in Brussels on March 22, 2016. Airlines cancelled hundreds of flights and European railways froze links with Brussels after a series of bomb blasts killed around 35 people in the city's airport and a metro train, sparking a broad security response. AFP PHOTO / KENZO TRIBOUILLARDKENZO TRIBOUILLARD/AFP/Getty Images

A Belgian soldier speaks to a police officer outside Brussels Central Station as people are allowed in small groups of ten to reach the station in order to take their commuter train following attacks in Brussels on March 22, 2016. Airlines cancelled hundreds of flights and European railways froze links with Brussels after a series of bombs blasts killed around 35 people in the city's airport and a metro train, sparking a broad security response. / AFP PHOTO / EMMANUEL DUNANDEMMANUEL DUNAND/AFP/Getty Images

A man puts a Belgian flag at a makeshift memorial at Place de la Bourse (Beursplein) following attacks in Brussels on March 22, 2016. Airlines cancelled hundreds of flights and European railways froze links with Brussels after a series of bomb blasts killed around 35 people in the city's airport and a metro train, sparking a broad security response. AFP PHOTO / KENZO TRIBOUILLARDKENZO TRIBOUILLARD/AFP/Getty Images

A man lights a candle at a makeshift memorial at Place de la Bourse (Beursplein) following attacks in Brussels on March 22, 2016. Airlines cancelled hundreds of flights and European railways froze links with Brussels after a series of bomb blasts killed around 35 people in the city's airport and a metro train, sparking a broad security response. AFP PHOTO / KENZO TRIBOUILLARDKENZO TRIBOUILLARD/AFP/Getty Images

A Belgian soldier patrols outside Brussels Central Station as people are allowed in small group of ten to reach the station in order to take their commuter train following attacks in Brussels on March 22, 2016.
Airlines cancelled hundreds of flights and European railways froze links with Brussels after a series of bombs blasts killed around 35 people in the city's airport and a metro train, sparking a broad security response. / AFP PHOTO / EMMANUEL DUNANDEMMANUEL DUNAND/AFP/Getty Images

The Belgian and European Union flags fly at half mast outside the embassy of Belgium in London, in the wake of coordinated bomb attacks on the main airport and the Metro system in Brussels. PRESS ASSOCIATION Photo. Picture date: Tuesday March 22, 2016. The attacks, condemned as "blind, violent and cowardly" by Belgian Prime Minister Charles Michel, came after the arrest in the city last week of terror mastermind Salah Abdeslam, who plotted November's Paris atrocity from the notorious Molenbeek suburb of Brussels. See PA story POLICE Brussels. Photo credit should read: Andrew Matthews/PA Wire

The Belgian flag flies at half mast above 10 Downing Street in London, in the wake of coordinated bomb attacks on the main airport and the Metro system in Brussels. PRESS ASSOCIATION Photo. Picture date: Tuesday March 22, 2016. The attacks, condemned as "blind, violent and cowardly" by Belgian Prime Minister Charles Michel, came after the arrest in the city last week of terror mastermind Salah Abdeslam, who plotted November's Paris atrocity from the notorious Molenbeek suburb of Brussels. See PA story POLICE Brussels. Photo credit should read: Stefan Rousseau/PA Wire

The Belgian flag flies at half mast above 10 Downing Street in London, in the wake of coordinated bomb attacks on the main airport and the Metro system in Brussels. PRESS ASSOCIATION Photo. Picture date: Tuesday March 22, 2016. The attacks, condemned as "blind, violent and cowardly" by Belgian Prime Minister Charles Michel, came after the arrest in the city last week of terror mastermind Salah Abdeslam, who plotted November's Paris atrocity from the notorious Molenbeek suburb of Brussels. See PA story POLICE Brussels. Photo credit should read: Stefan Rousseau/PA Wire

An Italian police officer patrols with a dog at Rome's Fiumicino aiport on March 22, 2016 as security measures were reinforced in the wake of attacks in Brussels.
European countries vowed to defend democracy against terrorism after blasts at Brussels airport and in the EU's institutional heart left at least 26 dead and dozens injured. / AFP PHOTO / TIZIANA FABITIZIANA FABI/AFP/Getty Images

The flags of Belgium and the European Union are seen flying on half mast reflected in the window of the Belgian embassy in Berlin on March 22, 2016.
People left tributes to the victims outside the embassy after a series of apparently coordinated blasts ripped through Brussels airport and a train. / AFP PHOTO / ODD ANDERSENODD ANDERSEN/AFP/Getty Images

Police officers patrol entrances to Rome's Fiumicino aiport on March 22, 2016, in the wake of the series of apparently coordinated explosions ripped through Brussels airport and a metro train, killing at least 26 people. Authorities in Europe have tightened security at airports, on subways, at the borders and on city streets after deadly attacks on the Brussels airport and its subway system. / AFP PHOTO / TIZIANA FABITIZIANA FABI/AFP/Getty Images

Travellers gather at Ryanair helping desk at Barcelona El Prat airport after the Brussels attacks, in Barcelona on March 22, 2016.
Europe froze air and rail links to Brussels as the authorities tightened security in alarm over a series of deadly bomb blasts that ripped through the Belgian capital's airport and a city-centre metro station.
/ AFP PHOTO / PAU BARRENAPAU BARRENA/AFP/Getty Images

The departure board at Rome's Fiumicino aiport displays the cancellation of flights to Brussels on March 22, 2016, in the wake of the series of apparently coordinated explosions ripped through Brussels airport and a metro train, killing at least 26 people. Authorities in Europe have tightened security at airports, on subways, at the borders and on city streets after deadly attacks on the Brussels airport and its subway system. / AFP PHOTO / TIZIANA FABITIZIANA FABI/AFP/Getty Images

The Belgian and European Union flags fly at half mast outside the embassy of Belgium in London, in the wake of coordinated bomb attacks on the main airport and the Metro system in Brussels. PRESS ASSOCIATION Photo. Picture date: Tuesday March 22, 2016. The attacks, condemned as "blind, violent and cowardly" by Belgian Prime Minister Charles Michel, came after the arrest in the city last week of terror mastermind Salah Abdeslam, who plotted November's Paris atrocity from the notorious Molenbeek suburb of Brussels. See PA story POLICE Brussels. Photo credit should read: Andrew Matthews/PA Wire

Travellers get informed at Ryanair helping desk at Barcelona El Prat airport after the Brussels attacks, in Barcelona on March 22, 2016.
Europe froze air and rail links to Brussels as the authorities tightened security in alarm over a series of deadly bomb blasts that ripped through the Belgian capital's airport and a city-centre metro station.
/ AFP PHOTO / PAU BARRENAPAU BARRENA/AFP/Getty Images

A boy holds a placard expressing sympathy for the victims of the terror attacks in Brussels during a protest at a makeshift camp at the Greek-Macedonian border near the village of Idomeni on March 22, 2016. Greece will not be able to start sending refugees back to Turkey from March 20, 2016, the government said, as the country struggles to implement a key deal aimed at easing Europe's migrant crisis. The numbers are daunting: officials said as of Saturday there were 47,500 migrants in Greece, including 8,200 on the islands and 10,500 massed at the Idomeni camp on the Macedonian border. / AFP PHOTO / ANDREJ ISAKOVICANDREJ ISAKOVIC/AFP/Getty Images

Travellers gather at Ryanair helping desk at Barcelona El Prat airport after the Brussels attacks, in Barcelona on March 22, 2016.
Europe froze air and rail links to Brussels as the authorities tightened security in alarm over a series of deadly bomb blasts that ripped through the Belgian capital's airport and a city-centre metro station.
/ AFP PHOTO / PAU BARRENAPAU BARRENA/AFP/Getty Images

A wreath is layed on a table along flowers and a candle inside the Belgium embassy in Berlin on March 22, 2016 as the national and EU flag is reflected in the window.
People left tributes to the victims outside the embassy after a series of apparently coordinated blasts ripped through Brussels airport and a train. / AFP PHOTO / ODD ANDERSENODD ANDERSEN/AFP/Getty Images

Policemem stand guard near a security perimeter set in the Rue de la Loi near the Maalbeek subway station, in Brussels, on March 22, 2016, after an explosion killed at least 11 people, according to spokesman of Brussels' fire brigade A string of explosions rocked Brussels airport and a city metro station on Tuesday, killing at least 13 people, according to media reports, as Belgium raised its terror threat to the maximum level. / AFP PHOTO / PHILIPPE HUGUENPHILIPPE HUGUEN/AFP/Getty Images

Policemen and soldiers stand guard near a security perimeter set in the Rue de la Loi near the Maalbeek subway station, in Brussels, on March 22, 2016, after an explosion killed at least 11 people, according to spokesman of Brussels' fire brigade A string of explosions rocked Brussels airport and a city metro station on Tuesday, killing at least 13 people, according to media reports, as Belgium raised its terror threat to the maximum level. / AFP PHOTO / PHILIPPE HUGUENPHILIPPE HUGUEN/AFP/Getty Images

The blown out facade of the terminal is seen at Zaventem airport, one of the sites of two deadly attacks in Brussels, Belgium, Tuesday, March 22, 2016. Authorities in Europe have tightened security at airports, on subways, at the borders and on city streets after the attacks Tuesday on the Brussels airport and its subway system. (AP Photo/Peter Dejong)

A pilot and cabin crew are evacuated from Zaventem Airport in Brussels by bus after an explosion on Tuesday, March 22, 2016. Explosions, at least one likely caused by a suicide bomber, rocked the Brussels airport and subway system Tuesday, prompting a lockdown of the Belgian capital and heightened security across Europe. At least 26 people were reported dead. (AP Photo/Geert Vanden Wijngaert)

An Israeli airport security guard patrols with a dog in Ben Gurion airport near Tel Aviv, Israel, Tuesday, March 22, 2016. After the Brussels attacks, Israel briefly announced that all Israeli flights from Europe were canceled, then reinstated the flights, Israel Airports Authority spokesman Ofer Leffler said. Pini Schiff, former director of security at Ben-Gurion Airport, said the attack in the Brussels airport was a colossal failure of Belgian security, and he said the chances are very low that such a bombing could take place in Israels airport. Israel's Ben-Gurion Airport is considered among the most secure in the world, an outcome stemming from several Palestinian attacks on Israeli planes and travelers in the 1970s. (AP Photo/Ariel Schalit)

Police and rescue teams are pictured outside the metro station Maelbeek in Brussels, Tuesday, March 22, 2016. Explosions, at least one likely caused by a suicide bomber, rocked the Brussels airport and its subway system Tuesday, prompting a lockdown of the Belgian capital and heightened security across Europe. (AP Photo/Martin Meissner)

Travelers wait at the counter of Brussels airlines in Ben Gurion airport near Tel Aviv, Israel, Tuesday, March 22, 2016. After the Brussels attacks, Israel briefly announced that all Israeli flights from Europe were canceled, then reinstated the flights, Israel Airports Authority spokesman Ofer Leffler said. Pini Schiff, former director of security at Ben-Gurion Airport, said the attack in the Brussels airport was a colossal failure of Belgian security, and he said the chances are very low that such a bombing could take place in Israels airport. Israel's Ben-Gurion Airport is considered among the most secure in the world, an outcome stemming from several Palestinian attacks on Israeli planes and travelers in the 1970s. (AP Photo/Ariel Schalit)

Smoke billows from the Zaventem Airport after a controlled explosion in Brussels, Tuesday, March 22, 2016. Bombs struck the Brussels airport and one of the city's metro stations Tuesday, killing and wounding dozens of people, as a European capital was again locked down amid heightened security threats. (AP Photo/Michel Spingler)

Police and rescue teams are pictured outside the metro station Maelbeek in Brussels, Tuesday, March 22, 2016. Explosions, at least one likely caused by a suicide bomber, rocked the Brussels airport and its subway system Tuesday, prompting a lockdown of the Belgian capital and heightened security across Europe. (AP Photo/Martin Meissner)

A man looks at flowers and a sign reading (Defy terror, protect freedom) outside the Belgium embassy in Berlin on March 22, 2016.
People left tributes to the victims outside the embassy after a series of apparently coordinated blasts ripped through Brussels airport and a train. / AFP PHOTO / ODD ANDERSENODD ANDERSEN/AFP/Getty Images

Rescue teams evacuate wounded people outside the Maalbeek metro station in Brussels on March 21, 2016 after a blast at this station located near the EU institutions.
Belgian firefighters said at least 26 people had died after "enormous" blasts rocked Brussels airport and a city metro station today, as Belgium raised its terror threat to the maximum level. / AFP PHOTO / --/AFP/Getty Images

Belgian police officers detain a man at the Gare du Midi train station in Brussels, Tuesday, March 22, 2016. Explosions, at least one likely caused by a suicide bomber, rocked the Brussels airport and its subway system Tuesday, prompting a lockdown of the Belgian capital and heightened security across Europe. (AP Photo/Michel Spingler)

Police dog handlers speak to travelers as they patrol after Eurostar train services were suspended on the Brussels route because of the attacks in Belgium, at St Pancras international railway station in London, Tuesday, March 22, 2016. Explosions, at least one likely caused by a suicide bomber, rocked the Brussels airport and subway system Tuesday, prompting a lockdown of the Belgian capital and heightened security across Europe. (AP Photo/Matt Dunham)

A Eurostar representative gives advice to a traveler after services were suspended on the Brussels Eurostar train route because of the attacks in Belgium, at St Pancras international railway station in London, Tuesday, March 22, 2016. Explosions, at least one likely caused by a suicide bomber, rocked the Brussels airport and subway system Tuesday, prompting a lockdown of the Belgian capital and heightened security across Europe. (AP Photo/Matt Dunham)

Picture taken with permission from the Facebook site of Jef Versele showing the aftermath of this morning's explosions at Brussels airport.

A police officers sets security perimeter near Maalbeek metro station, on March 22, 2016 in Brussels, after a blast at this station near the EU institutions caused deaths and injuries. AFP PHOTO / EMMANUEL DUNANDEMMANUEL DUNAND/AFP/Getty Images

BRUSSELS, BELGIUM - MARCH 22: Crew and passengers are evacuated from Zaventem Bruxelles International Airport after terrorist attacks on March 22, 2016 in Brussels, Belgium. At least 13 people are though to have been killed after Brussels airport was hit by two explosions whilst a Metro station was also targeted. The attacks come just days after a key suspect in the Paris attacks, Salah Abdeslam, was captured in Brussels. (Photo by Sylvain Lefevre/Getty Images)

BRUSSELS, BELGIUM - MARCH 22: Crew and passengers are evacuated from Zaventem Bruxelles International Airport after terrorist attacks on March 22, 2016 in Brussels, Belgium. At least 13 people are though to have been killed after Brussels airport was hit by two explosions whilst a Metro station was also targeted. The attacks come just days after a key suspect in the Paris attacks, Salah Abdeslam, was captured in Brussels. (Photo by Sylvain Lefevre/Getty Images)

Firefighters arrive at the scene near Maalbeek metro station, on March 22, 2016 in Brussels, after a blast at this station near the EU institutions caused deaths and injuries. AFP PHOTO / EMMANUEL DUNANDEMMANUEL DUNAND/AFP/Getty Images

French Interior Minister Bernard Cazeneuve gives a statement after a meeting with French Prime Minister, French Defence Minister and French President following Brussels attacks on March 22, 2016 at the Elysee Palace in Paris. A string of explosions rocked Brussels airport and a city metro station on March 22, killing at least 21 people in apparently coordinated attacks, officials said. / AFP PHOTO / STEPHANE DE SAKUTINSTEPHANE DE SAKUTIN/AFP/Getty Images

French Interior Minister Bernard Cazeneuve gives a statement after a meeting with French Prime Minister, French Defence Minister and French President following Brussels attacks on March 22, 2016 at the Elysee Palace in Paris. A string of explosions rocked Brussels airport and a city metro station on March 22, killing at least 21 people in apparently coordinated attacks, officials said. / AFP PHOTO / STEPHANE DE SAKUTINSTEPHANE DE SAKUTIN/AFP/Getty Images

A police officers sets a security perimeter near Maalbeek metro station, on March 22, 2016 in Brussels, after a blast at this station near the EU institutions caused deaths and injuries. AFP PHOTO / EMMANUEL DUNANDEMMANUEL DUNAND/AFP/Getty Images

Belgian servicemen and police officers block the road outside the Prime Minister's office where a meeting of the National Security Council is held, in Brussels, on March 22, 2016, after a string of explosions rocked Brussels airport and a city metro station, killing at least 21 people, as Belgium raised its terror threat to the maximum level.
The blasts come days after the dramatic arrest in Brussels on March 18 of Salah Abdeslam, the prime suspect in the Paris terror attacks that killed 130 people in November, after four months on the run. / AFP PHOTO / Belga / James Arthur Gekiere / Belgium OUTJAMES ARTHUR GEKIERE/AFP/Getty Images

Policemen speak at a security perimeter near Maalbeek metro station, on March 22, 2016 in Brussels, after a blast at this station near the EU institutions caused deaths and injuries. AFP PHOTO / EMMANUEL DUNANDEMMANUEL DUNAND/AFP/Getty Images

French Interior Minister Bernard Cazeneuve gives a statement after a meeting with French Prime Minister, French Defence Minister and French President following Brussels attacks on March 22, 2016 at the Elysee Palace in Paris. A string of explosions rocked Brussels airport and a city metro station on March 22, killing at least 21 people in apparently coordinated attacks, officials said. / AFP PHOTO / STEPHANE DE SAKUTINSTEPHANE DE SAKUTIN/AFP/Getty Images

First aid workers arrive atr Maalbeek metro station, on March 22, 2016 in Brussels, after a blast at this station near the EU institutions caused deaths and injuries. AFP PHOTO / EMMANUEL DUNANDEMMANUEL DUNAND/AFP/Getty Images

French Interior Minister Bernard Cazeneuve gives a statement after a meeting with French Prime Minister, French Defence Minister and French President following Brussels attacks on March 22, 2016 at the Elysee Palace in Paris. A string of explosions rocked Brussels airport and a city metro station on March 22, killing at least 21 people in apparently coordinated attacks, officials said. / AFP PHOTO / STEPHANE DE SAKUTINSTEPHANE DE SAKUTIN/AFP/Getty Images

Belgian servicemen and police officers block the road outside the Prime Minister's office where a meeting of the National Security Council is held, in Brussels, on March 22, 2016, after a string of explosions rocked Brussels airport and a city metro station, killing at least 21 people, as Belgium raised its terror threat to the maximum level.
The blasts come days after the dramatic arrest in Brussels on March 18 of Salah Abdeslam, the prime suspect in the Paris terror attacks that killed 130 people in November, after four months on the run. / AFP PHOTO / Belga / JAMES ARTHUR GEKIERE / Belgium OUTJAMES ARTHUR GEKIERE/AFP/Getty Images

First aid workers arrive atr Maalbeek metro station, on March 22, 2016 in Brussels, after a blast at this station near the EU institutions caused deaths and injuries. AFP PHOTO / EMMANUEL DUNANDEMMANUEL DUNAND/AFP/Getty Images

Policemen stand guard at the entrance of a security perimeter set near Maalbeek metro station, on March 22, 2016 in Brussels, after a blast at this station near the EU institutions caused deaths and injuries. AFP PHOTO / EMMANUEL DUNANDEMMANUEL DUNAND/AFP/Getty Images

An armed policeman secures the access to the terminal area of the Frankfurt Airport, on March 22, 2016, in Frankfurt, western Germany.
The increased security comes in the wake of the explosions in Brussels, according to several media have claimed more lives. / AFP PHOTO / DPA / Boris Roessler / Germany OUTBORIS ROESSLER/AFP/Getty Images

Policemen stand guard at the entrance of a security perimeter set near Maalbeek metro station, on March 22, 2016 in Brussels, after a blast at this station near the EU institutions caused deaths and injuries. AFP PHOTO / EMMANUEL DUNANDEMMANUEL DUNAND/AFP/Getty Images

An armed policeman secures the access to the terminal area of the Frankfurt Airport, on March 22, 2016, in Frankfurt, western Germany.
The increased security comes in the wake of the explosions in Brussels, according to several media have claimed more lives. / AFP PHOTO / DPA / Boris Roessler / Germany OUTBORIS ROESSLER/AFP/Getty Images

Emergency workers arrive at a security perimeter set near Maalbeek metro station, on March 22, 2016 in Brussels, after a blast at this station near the EU institutions caused deaths and injuries. AFP PHOTO / EMMANUEL DUNANDEMMANUEL DUNAND/AFP/Getty Images

A police officers sets a security perimeter near Maalbeek metro station, on March 22, 2016 in Brussels, after a blast at this station near the EU institutions caused deaths and injuries. AFP PHOTO / EMMANUEL DUNANDEMMANUEL DUNAND/AFP/Getty Images

A police officers sets a security perimeter near Maalbeek metro station, on March 22, 2016 in Brussels, after a blast at this station near the EU institutions caused deaths and injuries. AFP PHOTO / EMMANUEL DUNANDEMMANUEL DUNAND/AFP/Getty Images

Police officers walk past as a group of travelers stand together, after services were suspended on the Brussels Eurostar train route because of the attacks in Belgium, at St Pancras international railway station in London, Tuesday, March 22, 2016. Authorities locked down the Belgian capital on Tuesday after explosions rocked the Brussels airport and subway system, killing at least 13 people and injuring many more. (AP Photo/Matt Dunham)

Passengers are evacuated from Brussels airport, on March 22, 2016 in Zaventem, after at least 13 people were killed and 35 injured as twin blasts rocked the main terminal of Brussels airport.AFP PHOTO / JOHN THYSJOHN THYS/AFP/Getty Images

Passengers are evacuated from Brussels airport, on March 22, 2016 in Zaventem, after at least 13 people were killed and 35 injured as twin blasts rocked the main terminal of Brussels airport.AFP PHOTO / JOHN THYSJOHN THYS/AFP/Getty Images

Passengers board a bus as they evacuate the Brussels Airport in Zaventem, on March 22, 2016, after a string of explosions rocked Brussels airport and a city metro station, killing at least 21 people, as Belgium raised its terror threat to the maximum level. The blasts come days after the dramatic arrest in Brussels on March 18 of Salah Abdeslam, the prime suspect in the Paris terror attacks that killed 130 people in November, after four months on the run. AFP PHOTO / THIERRY MONASSETHIERRY MONASSE/AFP/Getty Images

Passengers are evacuated from Brussels airport, on March 22, 2016 in Zaventem, after at least 13 people were killed and 35 injured as twin blasts rocked the main terminal of Brussels airport.AFP PHOTO / JOHN THYSJOHN THYS/AFP/Getty Images

Passengers are evacuated from Brussels airport, on March 22, 2016 in Zaventem, after at least 13 people were killed and 35 injured as twin blasts rocked the main terminal of Brussels airport.AFP PHOTO / JOHN THYSJOHN THYS/AFP/Getty Images

Passengers are evacuated from Brussels airport, on March 22, 2016 in Zaventem, after at least 13 people were killed and 35 injured as twin blasts rocked the main terminal of Brussels airport.AFP PHOTO / JOHN THYSJOHN THYS/AFP/Getty Images

Passengers are evacuated from Brussels airport, on March 22, 2016 in Zaventem, after at least 13 people were killed and 35 injured as twin blasts rocked the main terminal of Brussels airport.AFP PHOTO / JOHN THYSJOHN THYS/AFP/Getty Images

Firefighters arrive at a security perimeter set near Maalbeek metro station, on March 22, 2016 in Brussels, after a blast at this station near the EU institutions caused deaths and injuries. AFP PHOTO / EMMANUEL DUNANDEMMANUEL DUNAND/AFP/Getty Images

Passengers evacuate the Brussels Airport in Zaventem, on March 22, 2016, after a string of explosions rocked Brussels airport and a city metro station, killing at least 21 people, as Belgium raised its terror threat to the maximum level. The blasts come days after the dramatic arrest in Brussels on March 18 of Salah Abdeslam, the prime suspect in the Paris terror attacks that killed 130 people in November, after four months on the run. AFP PHOTO / THIERRY MONASSETHIERRY MONASSE/AFP/Getty Images

Closed off road between Maelbeek station and Arts-Loi in Brussels. Pic: Shigeo Sugimoto/PA Wire

A victim receives first aid by rescuers, on March 22, 2016 near Maalbeek metro station in Brussels, after a blast at this station near the EU institutions caused deaths and injuries. AFP PHOTO / EMMANUEL DUNANDEMMANUEL DUNAND/AFP/Getty Images

A victim receives first aid by rescuers, on March 22, 2016 near Maalbeek metro station in Brussels, after a blast at this station near the EU institutions caused deaths and injuries. AFP PHOTO / EMMANUEL DUNANDEMMANUEL DUNAND/AFP/Getty Images

A security perimeter has been set, on March 22, 2016 near Maalbeek metro station in Brussels, after a blast at this station near the EU institutions caused deaths and injuries. AFP PHOTO / EMMANUEL DUNANDEMMANUEL DUNAND/AFP/Getty Images

A picture shows damage to the facade of Brussels Airport, in Zaventem, on March 2016 after two explosions in the airport. Belgian firefighters said there were at least 21 dead after "enormous" blasts hit Brussels airport and the city's metro system. / AFP PHOTO / BELGA / DIRK WAEM / Belgium OUTDIRK WAEM/AFP/Getty Images

A victim receives first aid by rescuers, on March 22, 2016 near Maalbeek metro station in Brussels, after a blast at this station near the EU institutions caused deaths and injuries. AFP PHOTO / EMMANUEL DUNANDEMMANUEL DUNAND/AFP/Getty Images

Policemen stand guard at the entrance of a security perimeter set near Maalbeek metro station, on March 22, 2016 in Brussels, after a blast at this station near the EU institutions caused deaths and injuries. AFP PHOTO / EMMANUEL DUNANDEMMANUEL DUNAND/AFP/Getty Images

Policemen stand guard at the entrance of a security perimeter set near Maalbeek metro station, on March 22, 2016 in Brussels, after a blast at this station near the EU institutions caused deaths and injuries. AFP PHOTO / EMMANUEL DUNANDEMMANUEL DUNAND/AFP/Getty Images

A picture taken on March 22, 2016 shows a Belgian emergency vehicle driving past passengers evacuating the Brussels Airport of Zaventem, after a string of explosions rocked Brussels airport and a city metro station, killing at least 21 people, as Belgium raised its terror threat to the maximum level. AFP PHOTO / JOHN THYSJOHN THYS/AFP/Getty Images

A helicopter of the Belgian police flies above the area near Maalbeek metro station, on March 22, 2016 in Brussels, after a blast at this station near the EU institutions caused deaths and injuries. AFP PHOTO / EMMANUEL DUNANDEMMANUEL DUNAND/AFP/Getty Images

Policemen and soldier stand guard at the entrance of a security perimeter set near Maalbeek metro station, on March 22, 2016 in Brussels, after a blast at this station near the EU institutions caused deaths and injuries. AFP PHOTO / EMMANUEL DUNANDEMMANUEL DUNAND/AFP/Getty Images

A picture taken on March 22, 2016 shows passengers waiting in a bus as they evacuate the Brussels Airport of Zaventem, after a string of explosions rocked Brussels airport and a city metro station, killing at least 21 people, as Belgium raised its terror threat to the maximum level. AFP PHOTO / JOHN THYSJOHN THYS/AFP/Getty Images

Policemen stand guard at the entrance of a security perimeter set near Maalbeek metro station, on March 22, 2016 in Brussels, after a blast at this station near the EU institutions caused deaths and injuries. AFP PHOTO / EMMANUEL DUNANDEMMANUEL DUNAND/AFP/Getty Images

The military police carries extra patrols at Schiphol Airport in Amsterdam, on March 22, 2016 in response to the attacks in the departure hall of Brussels Airport and at a Brussels metro station. / AFP PHOTO / ANP / Evert Elzinga / Netherlands OUTEVERT ELZINGA/AFP/Getty Images

A picture taken on March 22, 2016 shows passengers boarding a bus as they evacuate the Brussels Airport of Zaventem, after a string of explosions rocked Brussels airport and a city metro station, killing at least 21 people, as Belgium raised its terror threat to the maximum level. AFP PHOTO / JOHN THYSJOHN THYS/AFP/Getty Images

A picture taken on March 22, 2016 shows a Belgian police vehicle driving past passengers who are evacuating the Brussels Airport of Zaventem. Getty Images

In this photo provided by Georgian Public Broadcaster and photographed by Ketevan Kardava a man is wounded in Brussels Airport in Brussels, Belgium, after explosions were heard Tuesday, March 22, 2016. (Ketevan Kardava/ Georgian Public Broadcaster via AP)

Passengers are gathered near Brussels airport, on March 22, 2016 in Zaventem, following its evacuation after at least 13 people were killed and 35 injured as twin blasts rocked the main terminal of Brussels airport.AFP PHOTO / JOHN THYSJOHN THYS/AFP/Getty Images

Two passengers wait, on March 22, 2016 near Brussels airport in Zaventem , following its evacuation after at least 13 people were killed and 35 injured as twin blasts rocked the main terminal of Brussels airport.AFP PHOTO / JOHN THYSJOHN THYS/AFP/Getty Images

Passengers leave with their luggages, on March 22, 2016 near Brussels airport in Zaventem , following its evacuation after at least 13 people were killed and 35 injured as twin blasts rocked the main terminal of Brussels airport.AFP PHOTO / JOHN THYSJOHN THYS/AFP/Getty Images

Belgium police officers block a street in Brussels on March 22, 2016 after an explosion occurred at a metro station.
At least 13 people have been killed after two explosions occurred this morning in the departure hall of Brussels Airport. The Brussels metro stations have been evacuated after explosions at Schuiman and Maelbeek-Maalbeek. Government sources speak of a terrorist attack. The terrorist threat level has been heightened to four across the country. / AFP PHOTO / BELGA / PHILIPPE FRANCOIS / Belgium OUTPHILIPPE FRANCOIS/AFP/Getty Images

Passengers leave with their luggages, on March 22, 2016 near Brussels airport in Zaventem , following its evacuation after at least 13 people were killed and 35 injured as twin blasts rocked the main terminal of Brussels airport.AFP PHOTO / JOHN THYSJOHN THYS/AFP/Getty Images

Passengers gather, on March 22, 2016 near Brussels airport in Zaventem , following its evacuation after at least 13 people were killed and 35 injured as twin blasts rocked the main terminal of Brussels airport.AFP PHOTO / JOHN THYSJOHN THYS/AFP/Getty Images

A passenger waits, on March 22, 2016 near Brussels airport in Zaventem , following its evacuation after at least 13 people were killed and 35 injured as twin blasts rocked the main terminal of Brussels airport.AFP PHOTO / JOHN THYSJOHN THYS/AFP/Getty Images

A passenger waits, on March 22, 2016 near Brussels airport in Zaventem , following its evacuation after at least 13 people were killed and 35 injured as twin blasts rocked the main terminal of Brussels airport.AFP PHOTO / JOHN THYSJOHN THYS/AFP/Getty Images

Passengers who were evacuated from the airport wait in Zaventem, on March 22, 2016, after a string of explosions rocked Brussels airport of Zaventem and a city metro station, killing at least 13 people, according to media reports, as Belgium raised its terror threat to the maximum level. / AFP PHOTO / Belga / SEPPE KNAPEN / Belgium OUTSEPPE KNAPEN/AFP/Getty Images

Passsengers wait, on March 22, 2016 near Brussels airport in Zaventem , following its evacuation after at least 13 people were killed and 35 injured as twin blasts rocked the main terminal of Brussels airport.AFP PHOTO / JOHN THYSJOHN THYS/AFP/Getty Images

This view taken on March 22, 2016 shows the broken glasses at Brussels Airport in Zaventem after a two explosions targeted the main hall. A string of explosions rocked Brussels airport and a city metro station today, killing at least 13 people, according to media reports, as Belgium raised its terror threat to the maximum level. / AFP PHOTO / BELGA / JONAS ROOSENSJONAS ROOSENS/AFP/Getty Images

People walk on a blocked highway near Zaventem, leading to Brussels National airport, on March 22, 2016 after two explosions rocked the main hall of Brussels Airport, killing at least one person and wounding several others, officials said. AFP PHOTO / THIERRY MONASSETHIERRY MONASSE/AFP/Getty Images

A photo shows cars on a blocked highway near Zaventem, leading to Brussels National airport, on March 22, 2016 after two explosions rocked the main hall of Brussels Airport, killing at least one person and wounding several others, officials said. AFP PHOTO / THIERRY MONASSETHIERRY MONASSE/AFP/Getty Images

Brussels airport. Pic Bart van Meele/PA Wire

A photo taken on March 22, 2016 shows Brussels Airport, in Zaventem, after two explosions rocked the main hall of the airport, killing at least one person and wounding several others.
The Brussels metro service was being shut down on March 22, its operator said, following a blast at a station close to the capital's European quarter. / AFP PHOTO / BELGA / Belgium OUT/AFP/Getty Images

The scene at Brussels Airport. Pic Stephanie Vanhemelryck/PA Wire

The scene at Brussels Airport after two explosions were heard. Pic: Stephanie Vanhemelryck/PA Wire

The scene at Brussels Airport after two explosions were heard. Pic: Stephanie Vanhemelryck/PA Wire

A picture taken on March 22, 2016 shows smoke rising from the Maalbeek underground, in Brussels, following a blast at the station close to the capital's European quarter. Pic Getty Images

A photo shows cars on a blocked highway near Zaventem, Brussels National airport, on March 22, 2016 after two explosions rocked the main hall of Brussels Airport, killing at least one person and wounding several others, officials said. AFP PHOTO / THIERRY MONASSETHIERRY MONASSE/AFP/Getty Images

The scene at Brussels Airport after two explosions were heard. Pic: @davidcrunelle/PA Wire

The scene at Brussels Airport after. Pic @davidcrunelle/PA Wire

The scene at Brussels Airport after two explosions were heard. Pic @davidcrunelle/PA Wire

The aftermath of this morning's explosions at Brussels airport. Pic: Jef Versele/PA Wire

The aftermath of this morning's explosions at Brussels airport. Pic Jef Versele/PA Wire
NOTE TO EDITORS: This handout photo may only be used in for editorial reporting purposes for the contemporaneous illustration of events, things or the people in the image or facts mentioned in the caption. Reuse of the picture may require further permission from the copyright holder.

The aftermath of this morning's explosions at Brussels airport. Pic: Jef Versele/PA Wire

In this image provided by Daniela Schwarzer, smoke is seen at Brussels airport in Brussels, Belgium, after explosions were heard Tuesday, March 22, 2016. (Daniela Schwarzer via AP)

Salah Abdeslam

The first impulse of many on hearing news of the bombs in Brussels was to damn the bombers as 'sick', 'evil', 'twisted'.

That is similar to some of the language used about republican dissidents who killed prison officer Adrian Ismay.

On Nolan Live, Shaun Woodward, a former secretary of state for Northern Ireland described them as 'degenerate' and Paul Givan, a DUP MLA said they were 'subhuman'.

On that same programme I protested against the use of this language.

There are strategic as well as moral reasons why we shouldn't dismiss anyone, however cruel in such a way.

The first is that you are not going to get them to listen to you if you have already decided that they are beneath you, and wouldn't understand your superior compassion and intelligence.

There will be intelligence operatives and others trying to grasp what these people are up to, and none of them will be starting from the premise that they are 'evil' and 'sick'.

They will presume that they have motives, however bizarre, that in different circumstances they would be acting differently.

None of this should surprise anyone here.

One of the ironies pointed to on social media yesterday was that former IRA bomber Martina Anderson was rerouted away from Brussels, as part of the security crackdown, not because she was seen as a threat, but just as part of the general clampdown.

No one in Brussels is afraid of Ms Anderson any more.

And after the bombing of Adrian Ismay, much was made of how the dissidents in prison had smoked cigars to celebrate. But do we really believe that the reformed bombers of the Provisional IRA were much more mannered and restrained?

I have been in bars in Belfast where almost all the customers rose from their seats to cheer at the sound of a bomb going off.

The dissidents of today and the jihadis of IS like the Provos and UDA of the past can be trusted to have a high opinion of themselves too.

In the case of the dissidents, there is a logic, though we may not like it.

They want to preserve the flame of republican armed resistance.

They are not daft enough to think that they can overthrow the state and unite Ireland, but they want to keep the tradition of preparedness alive.

That's what the IRA was doing before the Troubles in the mid-1960s, when they only had a couple of dozen members in Belfast.

Brussels, like Paris in November, has been attacked by a group of jihadis, battle-hardened in Syria. These men have seen a lot of people die and do not have a high expectation of living long themselves.

And they want the West to get a taste of what their war is like, because they think we blithely vote for wars and as blithely stay out of them, never knowing the cost of the decisions we let our politicians take.

A response that says these people are 'subhuman' will be read as extending to thousands, perhaps millions of jihadis and their supporters and apologists.

It rings of a presumption that we are better than they, and they don't believe that.

Which leads to the question: how do we translate insight into their thinking, if we could gain it, into a strategic advantage over them?

The only thing that is going to work is intelligence gathering, and that is closed off in large part because the communities in which these guys live don't hand them over, feel included in our derision. Now where have we seen that before?

The lesson from Northern Ireland's past is that a community which feels estranged from the state will not be easy to penetrate. Therefore the state has to demonstrate to those communities that they are understood.

That starts by presuming they are human, galling and difficult as that might be.